1. Field of the Invention
The present invention relates, in general, to the fixation of bone fractures and, more particularly, to the fixation of bone fractures having small fragments proximate a terminal end of a bone.
2. Description of Related Art
Plates and screws are well accepted techniques for fixation of fractures. The standard bone plate is a planar bar of material, usually metal, having circular and/or slotted holes through which bone screws are placed. The bone plate is used to span a fracture and fixation screws are placed through holes in the bone plate positioned on either side of the fracture to secure the bone fragments the plate.
One variation of the standard bone plate is to modify the configuration of the screw holes to help provide compression across the fracture as the screw is placed. Another variation is to include female threads within the perimeter of the bone plate's screw holes, engaging male threads on the head of the screw to lock the screw to the plate.
Difficulties in using bone plates may arise in certain fractures occurring relatively close to the end of a bone, creating a relatively small end fragment. In this situation, there may simply be not enough bone available in the end fragment to accommodate a sufficient number of screws to achieve secure fixation. As a result, a surgeon using a conventional bone plate may use a suboptimal number of screws, which can lead to postoperative failure.
One example of a fracture occurring relatively close to the end of a bone is a fracture of the lateral malleolus, the terminal portion of the fibula that is present on the outside of the ankle, occurring close to its tip. In such situations, only a very small distal fragment may be present, providing inadequate room for more than one or two screws to be placed. Moreover, since the deep portion of this bone is a part of the overall ankle joint, screws cannot be placed through both cortices, as is commonly practice with plate/screw techniques. Accordingly, the surgeon may be faced with the undesirable situation of having the patient leave the operating room with only one or two screws engaging a bone surface directly under a bone plate.
In the past, one technique surgeons have used in an attempt to provide enhanced fixation or grip of a small terminal bone fragment is to begin with a standard plate and cut the plate transversely across at its last screw hole. Using a pair of surgical pliers or other suitable instrument, the remaining bone plate material on opposing sides of the partially remaining hole is bent around the outer surface of the terminal bone fragment. To some degree, this helps supplement the tenuous fixation provided by only one or two screws in the small terminal fragment. However, this terminal bone fragment may still remain far from being well secured.
In another previous technique disclosed in “Use of Zuelzer Hook Plate in the Treatment of Olecranon Fractures” by Wesely, Barenfeld, and Eisenstein, The Journal of Bone & Joint Surgery, Volume 58-A, Issue No 6, September 1976, pages 859-863, a further modification of this technique is described in which a flat plate is pre-contoured with two hooks at one end. The hooks are bent so that they are parallel to the longitudinal axis of the flat plate. The plate is applied to a fractured bone such as the olecranon by manually pressing the hooks into the bone and fixing the plate to the bone surface with screws. Although this technique adds the theoretical advantage of penetration of the terminal fragment with the hooks, if this plate is applied to an anatomic site in which the bone flares out at the terminal end, since the hooks are parallel to the linear axis of the plate, as the hooks are impacted, the plate will not sit flush with the bone surface past the flare at the terminal end but rather come to lie in a position that sits off the bone. In addition, this technique does not address the problem of creating holes in the bone at the correct depth for engagement by the hooks, but rather relies on manual pressure on the plate to attempt penetration of the bone by the hooks at whatever level they happen to contact. As can be noted by the examples in this article, the hooks may fail to penetrate the bone resulting in less than satisfactory engagement and fixation of the terminal fragment by the hooks as well as prominence of the hooks in the soft tissue because of incomplete seating. Finally, since these implants have hooks that extend an equal distance from the end of the plate, this design does not allow completely seating of both hooks in the common situation in which the bone surface at the terminal end is at an angle to the plane that is perpendicular to the long axis of the bone.
Distal radius fractures (what is often meant when using the term ‘wrist fracture’) are common injuries. These fractures are often comminuted and unstable. It is of importance in addressing such fractures to restore a smooth, anatomic and congruent articular surface with enough stability so that it does not displace during healing. In other locations in the body one objective of internal fixation is to produce compression between stable and unstable fragments in order to promote healing. However, in the case of the distal radius fractures, fixation that would produce this type of compressive loads between the articular fragments and the shaft may result in migration of the fragments, loss of length, malunions and failure. For this reason, the tenets of internal fixation for distal radius fractures are different, aimed at achieving a stable anatomic reduction while maintaining the joint surface in space supported out to length.
Recently, surgical fixation has become the procedure of choice for many of these unstable distal radius fractures. One common method of fixation is to apply a plate to the volar surface of the radius, with a locked fixed angle support behind the bone under the articular surface. As load is applied to the end of the bone during healing, the fixed struts under the articular surface prevent setting of the articular surface into the soft bone at the end of the radius and loss of fracture reduction and length.
An early design that used this approach was the SCS plate, manufactured by Small Bone Innovations, Inc. This plate has four tines that are integrally formed with the plate and bent at a right angle to the plane of the predominant distal surface of the plate. These tines functioned as fixed posts. However, there are certain shortcomings to this design. First, since there are four posts integrally formed with the plate, a somewhat cumbersome drill guide apparatus is required to be applied to the bone in order to drill the holes for all four posts simultaneously. This requires that the surgeon reduce the fracture (restore all fragments in space to a position that reflected normal anatomy of the bone) and then maintain it in position while the drill guide was applied, then removed, and the plate then applied. This can be significantly difficult to achieve. Another shortcoming that arises from the use of four fixed posts is that the drill guide cannot generally be moved during the drilling of each of the four holes. In addition, the surgeon is required to simultaneously align each of the four drilled holes with the corresponding leading tips of each of the four tines in order to get the plate inserted. Since this plate was intended to be a single size approach to variable fracture patterns, fracture elements didn't always line up in the optimal position for insertion of the tines. In other words, this design lacks the flexibility often required to avoid placing tines directly through fracture lines (which can push fragments apart, contributing to instability). These issues can lead to inadequate fixation.
A variation of the foregoing technique replaces the tines with pegs or screws, insertable at fixed angles through the body of the plate. This design has the advantage of allowing a surgeon to apply the plate and individually drill each hole and insert each peg separately, thus avoiding the difficulties associated with inserting four tines into drilled pilot holes simultaneously. However, this design still remains a one size fits all solution, and lacks flexibility to line up fixation for some complex fracture patterns. In addition, this design still requires that the anatomy be restored along the articular surface and held in place in order to apply the plate.
Another variation of this design is a plate that has fixation pegs that can be directed at a variety of angles, and then angularly locked into the plate. One example is the Volar Bearing Plate, manufactured by TriMed, Inc. Although this approach adds further flexibility to the direction of the fixation pegs, it still requires the surgeon to restore and hold the anatomy while the fixation is taking place, which can sometimes be difficult to perform. In addition, this design does not solve the problem of avoiding the placement of pegs through fracture lines, since the relative position of the peg holes is fixed, and moving the entry of one peg by shifting the plate to a different location results in corresponding movement of the placement locations of all of the other associated pegs.
Generally volar fixation plates need to be thick in cross-section in order to provide sufficient material to allow enough internal threads in the holes in order to securely lock the cooperatively threaded peg to the plate (whether at a fixed or variable angle). Since it is known that thick implants close to the rim of the distal radius may often cause irritation and even rupture of important tendons and other vital structures nearby, existing volar generally plates do not extend to the distal rim. As a result, small fractures of the distal volar rim are often not be secured by these plate designs, which can result in the fragment flipping over the edge of the plate, potentially causing catastrophic loss of reduction and dislocation of the carpal bones of the wrist.
Another approach to fixation of complex fractures uses a fragment specific technique. Generally, this method consists of individually securing each fragment separately with a specific implant. This can overcome the requirement that the surgeon hold the entire reduction in place, since each fragment can be reduced and fixed one at a time. One common implant used for this technique utilizes small plates with small fixed angle pegs, screws, or pins for purchase of the unstable fragment. These implants require the fragment to be reduced, the plate applied, and then the holes prepared and drilled followed by insertion and locking of the pegs, screws, or pins. These multiple steps can be somewhat difficult and time consuming, and may be an objection to application of this technique.
Another type of fragment specific implant uses wire forms or buttressing pins that penetrate fragments and hold it out to length. For example, the Volar Buttress Pin, manufactured by TriMed, Inc., is an implant that can be used to extend over the volar or dorsal rim. This implant is low profile and accordingly is unlikely to interfere with adjacent tendons or other vital structures. The buttress pin penetrates the fragment for fixation. However the surgical technique for this type of implant does require pre-drilling the holes for insertion of the legs of the buttress pin. These steps can be difficult to perform, often requiring surgeons with above average ability and experience. In addition, since these types of implants are a type of bent wire, they lack the strength and rigidity of larger plates.
Hook plates are implants that have been used at other locations to address fixation of a small terminal fragment with little available osseous bone area to accommodate fixation screws. Although early designs such as the LCP Hook Plate manufactured by Synthes, Inc. wrap around the end of the bone, these types of implants do not achieve any internal purchase of the fragment to be secured, and may have very limited to no purchase overall, resulting in poor rotational stability and limited resistance to sideways drift of the terminal fragment.
The hook plates of the present invention, configured for application to the lateral malleolus or the olecranon, achieve fixation of terminal fragments with two ‘teeth’ that provide rigid internal purchase of the fragment. These hook plates provide for rigid fixation of the terminal fragment and angular or translational movement under the plate. In addition, this type of plate promotes compressive load across the fracture which is intended for treatment at these locations.
For fixation of the distal radius, however, the configuration of these types of hook plates is not optimal, especially for fractures involving the volar or dorsal rim. Since hook plates of the present invention configured for application to the lateral malleolus or the olecranon promote compression against the stable fragment, in the case of distal radius fixation this would cause shortening of the fragment into the metaphyseal bone, and thus loss of articular reduction. The use of such hook plates is counterintuitive thus contraindicated for this type of internal fixation.
Accordingly, it is an object of the present invention to provide a bone plate that adequately secures a small bone fragment at a terminal end of a bone.
It is a further object of the present invention to provide a bone plate that can be seated flush against a bone characterized by a flare at the terminal segment, yet sill providing full engagement of the small terminal fragment by complete seating of one or more hooks into bone. It is a further object of the present invention to provide a means to create pilot holes in the terminal fragment for engagement by the hooks in the plate such that the hook or hooks in the plate engage the bone at the correct depth and trajectory so as to direct the plate to advance both longitudinally as well as drop down against the surface of the bone as it is seated.
It is another object of the present invention to provide a design that has a contour that approximates the flare of the terminal segment of a bone as well as provides one or more hooks that are angled along an axis that approximates the best linear fit approximation of such flare.
It is another object of the present invention to provide an implant to rigidly hold bone fragments proximate the volar rim, dorsal rim, or other area proximate to the articular surface of the distal radius, and to provide subchondral support of the articular surface to prevent loss of length.
It is another object of the present invention to provide an implant that resists shortening of bone fragments and acts like a buttress to the distal fragments.
It is another object of the present invention to provide an implant that resists application of bending torque directed to the base of the plate.
It is another object of the present invention to provide an implant that can be impacted without the need to pre-drill pilot holes in the bone proximate the fracture site.
It is another object of the present invention to provide implants having tines, or toothed members, positioned at various locations and individualized to a specific pattern of an injury.
It is another object of the present invention to provide a holder/impactor to securely grip a bone plate to be implanted, and to provide a striking surface to permit the surgeon to impact the tines of the bone plate directly into the distal radius.
It is another object of the present invention to provide a drill guide facilitating accurate placement of a bone plate proximate a terminal end of a bone.
These and other objects and features of the present invention will become apparent in view of the present specification, drawing and claims.